The human eye in its simplest terms functions to provide vision by transmitting light through a clear outer portion called the cornea, and focusing the image by way of a crystalline lens onto a retina. The quality of the focused image depends on many factors including the size and shape of the eye, and the transparency of the cornea and the lens. When age or disease causes the lens to become less transparent, vision deteriorates because of the diminished light which can be transmitted to the retina. This deficiency in the lens of the eye is medically known as a cataract. An accepted treatment for this condition is surgical removal of the lens and replacement of the lens function by an artificial intraocular lens (IOL). In the United States, the majority of cataractous lenses are removed by a surgical technique called phacoemulsification. During this procedure, an opening is made in the anterior capsule and a thin phacoemulsification cutting tip is inserted into the diseased lens and ultrasonically vibrated. The vibrating cutting tip liquefies or emulsifies the lens so that the lens may be aspirated out of the eye. The diseased lens, once removed, is replaced by an IOL.
A known difficulty for intraocular lenses has been that off-axis light rays can be reflected or transmitted into the visual field, producing undesirable photic effects. Edge designs for IOLs have been proposed to steer the unwanted light rays to different locations, but depending on the incident angle of the incoming light, this may not address the problem sufficiently and may inadvertently create new photic effects. The problems may be exacerbated in thin lens designs that use particular edge shapes for mechanical stability. There accordingly remains a need to reduce these undesired photic effects.